The fast increasing demand for wireless access to the Internet applications is fuelled by the remarkable growth of WiFi mobile devices, e.g., the smart-phones embedded with WiFi interfaces. However, the WiFi mobile devices typically consume lots of energy, e.g., the WiFi radio consumes about 1000 mW while transmitting/receiving data packets. Since the battery technology has not been developing fast enough to satisfy the demands, it is highly desirable to improve the energy efficiency or optimize the power consumption of wireless data communications on WiFi mobile devices for maximizing the battery life. Here, the WiFi mobile devices are mobile devices supporting wireless connection via WiFi.
Many WiFi mobile devices introduce Power Save Modes (PSM) to save power consumptions when there are no data packets transmitting/receiving. However, if multiple PSM clients connect to the same Access Point (AP) and wake up at the same time for the beacon to check for the presence of any buffered data packets with the same beacon interval at the AP, the data packets destined for different PSM clients will get queued in the AP's transmission queue resulting in longer waiting times for some of the PSM clients to retrieve the data packets.
In order to minimize the power consumption on WiFi mobile devices, most of existing solutions implement different scheduling strategies when a PSM client wakes up and notifies its AP.
Normal scheduling: queues all buffered data packets of a PSM client to the tail of the transmit queue. It increases the time PSM clients remain in the high power consumption Constantly Awake Mode (CAM), wasting energy.
High priority scheduling: queues the buffered data packets of a PSM client to a higher priority queue. While it helps reducing power consumption when the PSM client is competing with other CAM clients, it results in significant unfairness to the other CAM clients.
Additionally, since the scheduling mechanism cannot isolate PSM client(s) from other PSM clients, when an AP serves a certain PSM client, other PSM clients still need to keep an awakened state, which causes power consumption of the clients.
For example, comparing a case in which an AP serves four PSM clients and a case in which the AP serves one PSM client, in a common scheduling, the PSM clients triples the power consumption, while in a high priority scheduling, the PSM clients only increases 45% of the power consumption.